Inverter-Battery cable sizing - (4) 1 AWG DLO cables between Sol-Ark 15K to (2) EG4 Racks

[Axotopia]

Hi ALL,
new on forum, just putting together my system and wondering if I can get some advice on sizing cables from a Sol-Ark 15K to (2) battery racks ( w/(4) EG4 LifePower4 48V on each rack).

I am planning to use (4) 1 AWG DLO(RHH/RHW-2 listed) copper cables from the Sol-Ark 25K inverter to the bus bars at (2) EG4 battery racks (4-batteries each). Cable run is about 18-20ft between inverter and rack bus bars?

The 1 AWG DLO cables I am looking at are rated at Continuous 220A @ 90^C wet/dry per manufacturer, the Sol-Ark 15K has (2) pairs of terminal for battery connection (160A/pair, 275A/2-pairs), running (1) pair to each EG4 battery rack (4 batteries) appears to be sufficient in therory since the max per Sol-ark terminal is 160A per terminal pair. With 1 AWG (220A) cable, there should be a 37.5% amperage capacity overhead, and roughly a 1.0V drop over 20ft, vs 0.5V drop for a 4/0.

The DLO cables are quite pricy, so just want to do what is most effective for my budget. Also, since welding or automotive battery cables are not recognized cable designations by the National Electrical Code which my AHJ uses, I would likely fail my electrical inspection if I go with those.

Wondering if I am missing anything. Any feedback would be greatly appreciated. Thanks.

 

[pvgirl]

1 AWG is not sufficient, the 220 amp rating of 1 AWG is only vaild in free air, and at 90c. Conductors between your batteries and aol-ark will be running inside the racks and the sol-ark, and should be in conduit to be complaint with the NEC. Also the 90c ampacity can only be used if the devices are rated and marked for 90c conductors. Otherwise the standard ampacity tables, and 75c rating should be used. With the breakers rated for 200 amp on the breakers on the sol-ark using 3/0 or 4/0 wire. sol-ark manual recommends 4/0 conductors.

Fine stranded MTW is also acceptable under the NEC, such as https://www.wireandcableyourway.com/4-0-type-mtw-ul1284-wire-2109-strand This wire will need to be terminated with lugs rated for use with class K stranding.

 

[niktak11]

Too small. I went with 2/0 (2 pairs) for the 15ft run between my busbars and the sol-ark. That's the minimum I'd do for that distance.

 

[Axotopia]

Wondering what cable type everyone is using. Here's my confusion, does cable current capacity matters or does it boil down solely to wire size. For example .. for 4/0 @ 90^C Wet/Dry is roughly
XLP/XHHW-2/USE-2/RHH/RHW-2 Aluminum = 205A
XLP/XHHW-2/USE-2/RHH/RHW-2 Copper = 260A
DLO = 405A

.... 1 AWG DLO Cable is 220A ... which is better than 4/0 XLP/XHHW-2/USE-2/RHH/RHW-2 Aluminum (205A) and 2/0 XLP/XHHW-2/USE-2/RHH/RHW-2 Cooper (195A) with current capacity ...
and if I move up to 1/0 DLO (260A), it is about the same as 4/0 XLP/XHHW-2/USE-2/RHH/RHW-2 Copper

Sol-Ark 15K can only produce 160A if connected to 1 terminal pair ... so assuming that output is balanced when connected to 2 terminal pairs to get 275A, which is a lower 138A-ish per battery output channel. Feels like cables going beyond 200A per channel is a diminishing returns ... just theory on my end, thus the reality check with you folks on the forum.

 

[pvgirl]

NEC 2020 Table 310.16 Ampacities of Insulated Conductors in Raceway, Cable, or Earth (Directly Buried) is the table that matters for wire aka conductor amp capacity. NEC 2020 110.14(C) Temperature Limitations has notes on the use the various temperature ratings in table 310.16, generally that you can't use the 90c or higher column for sizing wires(unless you are derating). NEC 2020 310.4 Conductor Constructions and Applications covers what types of conductors you can use.

4/0 copper is going to 230amps rated per NEC, for any wire type with at least at 75c temp rating. Aluminum wire will be rated less.

 

[Axotopia]

NEC 2020 Table 310.16 Ampacities of Insulated Conductors in Raceway, Cable, or Earth (Directly Buried) is the table that matters for wire aka conductor amp capacity. NEC 2020 110.14(C) Temperature Limitations has notes on the use the various temperature ratings in table 310.16, generally that you can't use the 90c or higher column for sizing wires(unless you are derating). NEC 2020 310.4 Conductor Constructions and Applications covers what types of conductors you can use.

4/0 copper is going to 230amps rated per NEC, for any wire type with at least at 75c temp rating. Aluminum wire will be rated less.

Thanks for getting into the NEC, definitely a whole other world but great reference. Think I kinda get what you are saying ...

The DLO (also listed as RHH/RHW-2 for NEC compliance) rating is based on Table 310.17 [Ampacities of Single-Insulated Conductors in Free Air], which is 405A for 4/0 at 90^C, but 260A per NEC 310.16 [Ampacities of Insulated Conductors in Raceway, Cable, or Earth (Directly Buried)] if using the RHH/RHW-2 Type. So looks like 1/0 Cooper or 3/0 Aluminum will be bare minimum size for each pair of Sol-Ark battery terminal current (160A channel) as long as its 3 or less conductors per conduit. I current am putting in (2) 2" FMC with 2 conductors per conduit.

Now, If I parallel a pair of Sol-Ark 15K in the future, per Table 310.15(C)(1) [Adjustment Factors for More Than Three Current-Carrying Conductors].....then that would potentially end up with (4) conductor per conduit to handle (275A+275A), which means I will need to apply a 0.8 correction factor, ending up with (4) 3/0 Cooper or (4) 4/0 Aluminum per 2" FMC conduit.

Sorry to turn this into a Mike Holt forum, but think I am getting it ... or making it more confusing ...

EDIT: So based on this logic, to handle the Sol-Ark 15K full dual channel battery current of 275A with only (2) of conductors in conduit(s) instead of (4) 1/0 Cooper, cables will need to be 250kmil (XHHW-2/RHH/RHW-2) Copper at a minimum?

 

[pvgirl]

In determining the wire ampacity, we need to consider the breaker size on the sol-ark is 200amps per connection and we need to make sure our wire is properly sized for this protection, per NEC rules this would mean our wire needs to have an ampacity >175a. Additionally since the load of the sol-ark is continuous, per NEC we need to multiply the amps by 1.25, 275A * 1.25 = 344A, per connection that is 172A. Per 110.14 we must use the 75c rating. Requiring 3/0 copper or 4/0 aluminum.

When derating for more then 3 conductors, we can finally use the 90c column for RHW-2. So with 172 amps / 80% = 215amps, which using the 90c ampacity, we can still use 3/0 copper, but we would need to up size to 250 mcm for aluminum.

For a single connection we need to be above >350amps, based on the cicuit breker rating. which would 500mcm copper, and 600 mcm aluminum.

 

[niktak11]

The manual recommends 2/0 copper for the grid input and outputs, presumably because it will fall under dwelling ampacity for most setups.

 

[webbbn]

Shouldn't the wire be protected by breakers/fuses on the battery side, which would likely be smaller than 200A, since the inverter is only rated to pull 275A max over both wires?

 

[pvgirl]

Shouldn't the wire be protected by breakers/fuses on the battery side, which would likely be smaller than 200A, since the inverter is only rated to pull 275A max over both wires?

Each battery has a 100amp circuit breaker, 4 in parallel is 400amps on the battery side,=

 

[webbbn]

Each battery has a 100amp circuit breaker, 4 in parallel is 400amps on the battery side,=

Then if you don't add an additional breaker/fuse between that and a wire, you need your wires to support 400A, right? An upstream breaker in the inverter doesn't protect a wire if there's a short before the breaker.

 

[pvgirl]

Then if you don't add an additional breaker/fuse between that and a wire, you need your wires to support 400A, right? An upstream breaker in the inverter doesn't protect a wire if there's a short before the breaker.

The battery breakers will trip in most cases of shorts.

 

[webbbn]

The battery breakers will trip in most cases of shorts.

I'm not an electrician, but that doesn't seem like something code would allow.

In any case, my main point is that, you should be able to use smaller breakers on the battery side, since your load doesn't require 400A, and then you can use smaller wire.

 

[niktak11]

I've never seen someone put breakers on both sides of a DC wire run, but it kinda makes sense.

 

[webbbn]

I've never seen someone put breakers on both sides of a DC wire run, but it kinda makes sense.

Putting a breaker at the end of a wire doesn't make any sense. The breakers in the Sol Ark are protecting the inverter, not the wire.

It's the same as the breakers in a main breaker box, where you have the main breaker, which is protecting the box, and all the other breakers that are protecting the outgoing wires.

 

[niktak11]

Putting a breaker at the end of a wire doesn't make any sense. The breakers in the Sol Ark are protecting the inverter, not the wire.

It's the same as the breakers in a main breaker box, where you have the main breaker, which is protecting the box, and all the other breakers that are protecting the outgoing wires.

In your second example there is only one source of power. In the sol-ark scenario there are sources of power at either end of the battery cables.

 

[Axotopia]

In determining the wire ampacity, we need to consider the breaker size on the sol-ark is 200amps per connection and we need to make sure our wire is properly sized for this protection, per NEC rules this would mean our wire needs to have an ampacity >175a. Additionally since the load of the sol-ark is continuous, per NEC we need to multiply the amps by 1.25, 275A * 1.25 = 344A, per connection that is 172A. Per 110.14 we must use the 75c rating. Requiring 3/0 copper or 4/0 aluminum.

When derating for more then 3 conductors, we can finally use the 90c column for RHW-2. So with 172 amps / 80% = 215amps, which using the 90c ampacity, we can still use 3/0 copper, but we would need to up size to 250 mcm for aluminum.

For a single connection we need to be above >350amps, based on the cicuit breker rating. which would 500mcm copper, and 600 mcm aluminum.

Wow! You rock! Thanks for your detailed walk thru on the NEC, definitely a minefield for the DIY!

Sounds like (4) 3/0 Copper may be the bare minimum using the (2) pairs battery terminals in the Sol-Ark 15K inverter; or 500mcm Copper if using something like the HG Sol-Ark 15K Bus Bars.

 

[webbbn]

In your second example there is only one source of power. In the sol-ark scenario there are sources of power at either end of the battery cables.

Good point. I hadn't thought of charging current. In that case I guess it does make sense to fuse both end of a long battery connection.

 

[Oldphile]

Why does 310.12 state that 4/0 wire is suitable for 250 amp service?

 

[pvgirl]

Why does 310.12 state that 4/0 wire is suitable for 250 amp service?

Load diversity, a single residence is not going to be running all there loads simultaneously, and a reduced wire size is allowed. This section only applies to services/feeders serving the entire load of a single dwelling unit. Doesn't apply to this posts discussion of battery wire sizing.